WDPS31 PGTW 081500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 12P (GABRIELLE)  
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.8S 152.6E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 391 NM EAST OF CAIRNS, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 12P CONTINUES TO CONSOLIDATE WITH IMPROVED
CONVECTIVE BANDING EVIDENT IN BOTH ANIMATED ENHANCED INFRARED (EIR)
SATELLITE IMAGERY AND ANIMATED RADAR IMAGERY FROM WILLIS ISLAND.
EIR ALSO INDICATES AN INCREASE IN CENTRAL CONVECTION AND A
COINCIDENT BOOST IN POLEWARD OUTFLOW AS THE SYSTEM TAPS INTO AN
APPROACHING SHORTWAVE TROUGH THUS ENVIRONMENTAL CONDITIONS CONTINUE
TO IMPROVE. ALTHOUGH THE LOW-LEVEL CIRCULATION CENTER REMAINS
BROAD, THE CENTER IS WELL-DEFINED NORTHEAST OF LIHOU REEF, WHICH IS
REPORTING 30 TO 35 KNOT SUSTAINED (10-MINUTE AVERAGE) SOUTHEASTERLY
WINDS WITH GUSTS UP TO 45 TO 50 KNOTS. THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE BASED ON THE RADAR IMAGERY AND A
081132Z MHS 89GHZ MICROWAVE IMAGE. A PARTIAL 081130Z ASCAT-B IMAGE
CONTINUES TO REVEAL EXPANSIVE GALE-FORCE WINDS OVER THE EASTERN
PERIPHERY OF THE SYSTEM. THE 34-KNOT WIND RADII WERE ADJUSTED BASED
ON A DETAILED ANALYSIS OF THE 080745Z SMAP PASS.

INITIAL WIND RADII BASIS: SMAP DATA 

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR)
POSITIONED TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   APRF: T3.0 - 45 KTS
   CIMSS ADT: 45 KTS AT 081130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TC 12P WILL TRACK SOUTHWARD ALONG THE WESTERN
PERIPHERY OF THE STR THROUGH TAU 12. AFTER TAU 12, THE STR WILL
SHIFT TO THE NORTHEAST AS A DEEP TROUGH PROPAGATES OVER THE CORAL
SEA, WHICH WILL GENERALLY ACCELERATE THE SYSTEM SOUTHEASTWARD
WITHIN THE ENHANCED FLOW BETWEEN THE TROUGH AND THE STR. THERE IS A
SHORT 36-HOUR WINDOW FOR DEVELOPMENT WITH FAVORABLE CONDITIONS,
BEFORE THE SYSTEM INTERACTS WITH THE SHORTWAVE TROUGH AND
INCREASING VERTICAL WIND SHEAR (VWS). THEREFORE, THE PEAK INTENSITY
OF 75 KNOTS IS ANTICIPATED BY TAU 36 THEN STEADY WEAKENING THROUGH
THE REMAINDER OF THE FORECAST. TC 12P WILL SLOW AND UNDERGO
SUBTROPICAL TRANSITION AS IT NEARS NEW ZEALAND. VWS ASSOCIATED WITH
THE SUBTROPICAL JET WILL INCREASE TO 40 TO 60 KNOTS WHILE SST
VALUES COOL TO 24 TO 22C.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE REMAINS IN GOOD
AGREEMENT WITH A 105NM SPREAD IN SOLUTIONS AT TAU 72, LENDING HIGH
CONFIDENCE TO THE JTWC FORECAST TRACK. AFTER TAU 72, GUIDANCE
DIVERGES WITH A 155NM SPREAD IN SOLUTIONS AND INCREASING
UNCERTAINTY BY TAU 96. AS INDICATED IN THE 071800Z COAMPS-TC
ENSEMBLE, RAPID INTENSIFICATION (RI) IS POSSIBLE WITHIN THE NEXT 36
HOURS WITH PEAK PROBABILITIES OF 40 TO 50 PERCENT THROUGH TAU 24.
ADDITIONALLY, RAPID INTENSIFICATION AIDS HAVE TRIGGERED REFLECTING
A CONDUCIVE RI ENVIRONMENT CHARACTERIZED BY ROBUST POLEWARD
OUTFLOW, LOW VERTICAL WIND SHEAR AND WARM SST VALUES. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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